The agitation apparatus is an important unit operating equipment in chemical, biochemical and other engineering. Presently, agitation apparatus are generally stirred by one stage or multistage mechanical impellers to provide homogeneous mixing, dispersing, suspending and emulsifying to materials and thus to strengthen mass-transfer, heat-transfer, chemical reaction and biochemical reaction processes. However, although the impellers of conventional agitation apparatuses have been improved significantly, and disk radial turbine type, axial propeller type, scissors type or three-vane-sweepback blades or like have been developed, the basic flow of materials during stir still consists of vortex flow with the impeller shaft as vortex center, and vortex ring with circumferential streamline between solid vortex nucleus zone and vessel wall as a plurality of toroidal vortex, i.e., axial circulation of vortex ring flow on vertical plane. Besides, although combination of different impeller stage numbers and different impeller types can be used, and even supplemented by accessories as baffles and draft tube, only the magnitude of the relative static solid vortex nucleus zone and the shape, size and number of vortex rings may be changed. Because the streamline of the above two kinds of vortex is perpendicular or almost perpendicular to the velocity gradient, temperature gradient and concentration gradient, its effect on convection heat-transfer and mass-transfer is zero, hence the heat-transfer and mass-transfer in vortex nucleus will mainly rely on molecular diffusion.
The agitation power input needed is greatly increased due to the increase of the diameter and rotation rate of impeller, but the mixing effectiveness as well as the heat and mass transfer capability can not be obviously improved due to the mass, momentum and vorticity conservation of vortex, so that the exchange of heat and mass is constrained.
As a consequence of further increasing number, diameter and rotation rate of impeller there is an even greater need for power input to operate. Although the mixing performance as well as the heat and mass transfer has been infinitely improved, the productivity will still be lower than expectation corresponding to energy consumption.
In large tanks with vertical agitator assembly, the preferable method of reducing swirling is to provide baffles that impede rotational flow without interfering with radial or longitudinal flow. A simple and effective baffling is attained by installing vertical strips or rows of tubes to the wall of the tank at some angles. However, baffles always consume more power than the case without baffles, particularly for the operation at high Reynolds number. When high shear in the impeller itself is desired, draft tube is used to control the direction and velocity of current coming into the impeller. The power input of agitation will increase, owing to the velocity in the draft tube increasing.
For instance, in the diffusion controlled notification reaction of furacillin and reduction reaction of nitrobenzene, when the reaction heat at the toroidal vortex is unable to be effectively removed by stirring with conventional equipment and out of control, reactants will explode, whereas the nonuniformity in temperature will result in increasing by-products. In the polymerization reaction of polyvinyl chloride, the reaction heat is also difficult to be removed from the toroidal vortex even in suspended and emulsified solution, and the nonuniformity in temperature will lead to low productivity and difficulty in quality control. In biological reaction tanks such as those for fermentation, due to a difficult replenishment of oxygen required for aerobic fermentation in the toroidal vortex and a difficult removal of heat, the metabolism of bacteria is usually affected and thus the productivity and the product quantity is seriously decreased.
To sum up, the conventional agitation apparatuses can only rely on increasing the number of stirring impeller stages, decreasing vortex ring diameter and/or enlarging blade diameter and raising stirring rate, to achieve high shearing flow zone around blades and near the wall and to increase (or decrease) concentration and to raise (or to drop) temperature in the outmost streamline of vortex rings by turbulent diffusion. In this way, it is possible to raise the total amount of heat-transfer or mass-transfer, but impossible to raise tangibly and effectively the overall coefficient of heat-transfer or mass-transfer. Obviously, the conventional agitation apparatuses are poor in homogeneity of mixing, low in gloss coefficients of heat-transfer and mass-transfer, high in energy consumption, low in productivity and unstable in quality of products. In the China Patent No. CN1033528A (Application No. 87101299.5) by Zai-Li Xie (assigned to Zhejiang Petroleum-Chemical Designing Institute), a kind of fermentation tank is disclosed, which uses gas jet and venturi tube to mix gas and liquid and utilize mechanical energy of gas flow tangential velocity to lower the stirring power. However, the said patent is 1) necessary to work under the designed working condition, otherwise would obviously lower the mixing effect, and thus poor in operation flexibility; 2) unable to improve axial circulation of materials in the tank; 3) complex in structure and difficult in cleaning; 4) unable to improve homogeneity effectively.
In order to overcome above said defects, a plurality of static mixer means are independently and separately disposed in a traditional agitation apparatus. Said static mixer means is generally used in pipeline production having very short process time in prior art. The agitation apparatus is generally used in batch production having longer process time. Therefore, the mechanical energy of impeller or fluid media introduced into agitation apparatus make said static mixer means to work, the performance of agitation apparatus according to the invention is excellently improved.
Thus an agitation apparatus which can be used in aqueous fermentation process, polymerization process, monophase and multiphase chemical reaction controlled by diffusing process, mixing, dissolving, dispersing and extracting process in liquid media having higher productivity under far lower agitation power input, with considerably improved operation performance and increased operative flexibility, is highly desirable. Particularly, retrofit of existing agitation process vessel can be easily completed with far shorter pay-back period.